Blow molding die

ABSTRACT

Dies for forming hollow articles by blowing into a plasticated synthetic resin parison in a mold cavity formed in a pair of supplementary dies which are provided with means operable adjacent one end of the die cavities to force a limited amount of the parison toward one end of the mold cavity to insure the forming in one end of a hollow molded article a seam produced by pinching one end of a section of the parison from the oncoming supply thereof in such manner that the seam has a thickness no less than that of the portions of the article adjacent said seam.

United States Patent [1 Waterloo Aug. 21, 1973 [73] Assignee: GrahamEngineering Corporation,

York, Pa.

[22] Filed: Mar. 12, 1971 [21] Appl. No.: 123,596

[52] U.S. Cl. 425/387 [51] Int. Cl 1328b 11/08 [58] Field of Search425/326 B, 387 B,

[56] References Cited UNITED STATES PATENTS 3,209,401 10/1965 Mehnert425/387 B 3,424,829 1/1969 Peters et a]. 425/387 B 3,619,857 11/1971Gilbert 425/387 B Primary Examiner-Robert D. Baldwin AssistantExaminer-Brian P. Ross Attorney- C. Hercus Just 57] ABSTRACT Dies forforming hollow articles by blowing into a plasticated synthetic resinparison in a mold cavity formed in a pair of supplementary dies whichare provided with means operable adjacent one end of the die cavities toforce a limited amount of the parison toward one end of the mold cavityto insure the forming in one end of a hollow molded article a seamproduced by pinching one end of a section of the parison from theoncoming supply thereof in such manner that the seam has a thickness noless than that of the portions of the article adjacent said seam.

3 Claims, 5 Drawing Figures Patented Aug. 21, 1973 2 Sheets-Sheet lFIG.2

INVENTOR. William C. Waterloo BY A ORNE Y FIG. I

Patented Aug. 21, 1973 2 Sheets-Sheet :3

II IHI In] H \llllllllll FIG.3

PRIOR ART F IG 5 INVENTOR.

William C. Mbferloo A ORNE Y BLOW MOLDING rm:

BACKGROUND OF THE INVENTION The formation of hollow articles, such ascontainers, from thermoplastic synthetic resin by the formation of aparison which, in plasticated condition, is capable of being enclosedbetween a pair of mold dies while injecting air or other suitable gasinto a section of the parison, which is sealed at opposite ends, so asto expand the parison into conformity with the die cavity walls, iswidely practiced. In such procedure, the parison progressively movesfrom a parison-forming head for introduction between said pair ofmolding dies while the dies also are moving in the direction of theparison during the time the segregated section of the parison is beingblown as aforesaid to form containers, such as jars or the like, whichhave a bottom. During the foregoing procedure, the bottom of thecontainer is formed adjacent one end of the segregated portions of theparison which is pinched from the oncoming, continuouslyformed parison.

Said pinched end of the parison forms a seam, for example, in saidbottom of a container when formed by the foregoing procedure. However,incident to said section of the parison being pinched from the oncomingcontinuously formed parison, there is a tendency for said pinched end ofsaid section of the parison to be noticably thinner along the pinchedline which ultimately forms the seam in the aforementioned bottom ofsuch container, whereby along said seam, the bottom is not as thick asthe adjacent portions of the bottom of such a container. This is anundesirable characteristic of containers formed by such means in that itpresents a line of weakness.

Thus far, no ready solution has been found for avoiding theaforementioned tendency other than to increase the thickness of the wallsections of the parison which are to form such bottom of the container,whereby at least the thinned portion of the resulting bottom along saidseam will be adequate to withstand maximum stresses to which thecontainer is intended to be subjected. Obviously, this requiresproviding a thickness of resin in the bottom of such container in excessof that which normally would be required if, for example, the seam wereof equal thickness to that of the portions of the bottom of thecontainer adjacent said seam.

In order to obviate the foregoing difficulty, it is the principal objectof the present invention to provide means on the molding dies which areoperable to force a relatively small additional amount of the parisontoward the portion thereof which is pinched that ultimately forms theseam in a transverse end wall, such as the bottom of a container, so asto provide at least equal thickness along said seam as in the portionsof the transverse wall adjacent the seam.

It is another object of the invention to provide transversely extendingbars respectively upon the plurality of mold dies adjacent the rim meansof the die cavities which form such transverse end wall upon a hollowmolded resin article, said ribs being operable to squeeze and therebyforce an adjacent portion of the parison which is immediately exteriorof the die cavity toward said adjacent rim means and thereby increasethe volume of resin which is pinched by said rim means so as to beadequate to provide said desired thickness of seam portion in saidtransverse wall of a molded article.

It is a further object of the invention to form said transverse ribs onsaid dies with a squeezing or pinching surface that is wider than theadjacent rim means of the die in order to insure the forcing of anadequate amount of resin from the parison toward that portion thereofwhich is pinched by said rim means and thereby ensure an adequatethickness of seam in said transverse wall at one end of a molded articleformed by said die.

Further, other and additional objects of the invention will becomeapparent from the summary, detailed description, claims and drawingswhich follow hereinafter.

BRIEF SUMMARY OF THE INVENTION The principal improvement aspect of theinvention in contrast to conventional molding dies employed inblown-in-the-mold types of molding machine for forming hollow articlesfrom plasticated synthetic resin is the realization of the fact thatwhen rim means at opposite ends of molding die cavities simultaneouslypinch longitudinally spaced portions of a plasticated synthetic resinparison, a seam will be formed when the parison is blown into conformitywith the molding cavity of the dies and if one of said pinched portioncomprises a transverse wall of a hollow container, for example, saidwall will be thinner along the line of said seam than the adjacentportions of the wall but said difficulty may be obviated bysimultaneously modifying the amount of plastic adjacent the rim membersof the die cavities which effects such pinching so that a slightlygreater amount of plastics than otherwise would be provided is forcedbetween said rim members as they are closing upon each other to effectthe segregation of said section of parison from the oncoming tubularsupply thereof.

One effective means for furnishing such slightly additional volume ofresin to the segregated section of pari son which has been pinched fromthe oncoming supply thereof comprises the provision of a transverselyextending rib on each of the mold sections adjacent the trailing endsthereof and in slightly spaced relation to the adjacent rim means of thedie cavities, whereby the closing of the dies brings the opposing ribsinto squeezing relationship with opposite sides of the portion of theparison which is immediately exterior of the die cavities and therebyforces a limited amount of said parison between said adjacent rim meansof the die cavities while they are closing toward each other so as toprovide the aforementioned slightly additional amount of resin which isnecessary to avoid the customary difficulties described above.

In order to render the transverse ribs efiective, they should be of alength at least equal to the width of the parison when compressedbetween the opposing ribs respectively on the dies, in addition tohaving a width in a direction parallel to the axis of the parison whichis greater than the corresponding width of the adjacent rim means of thedie cavities in order to effect the desired degree of squeezing of saidparison.

The foregoing featues and characteristics of the invention whichcomprise additions to conventional molding dies and the method ofoperating the same to form hollow. articles in which any seams intransverse walls thereof are at least equal in thickness to the adjacentportion of said walls are set forth in the following detaileddescription, claims and drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an exemplary vertical sectionalelevation showing a parison head operable to discharge a parisonupwardly for disposition between molding dies which embody theprinciples of the invention.

FIG. 2 is a small scale diagrammatic side elevation view of the parisonextruder head and Ferris wheel on which the molds are mounted toillustrate the relative positions of these elements in accordance withthe invention.

FIG. 3 is a larger scale fragmentary elevation of one face of a moldingdie as seen on the line 3-3 of FIG. 1.

FIG. 4 is a fragmentary vertical sectional view of a pair of cooperatingmolding die sections generally as seen on the line 4-4 of FIG. 3 andillustrating on a larger scale than in FIG. 1 details of the invention.

FIG. 5 is a view similar to FIG. 4 but illustrating correspondingsections of conventional molding dies and showing in section theinherent deficiency in a molded article produced thereby.

DETAILED DESCRIPTION Referring to FIG. 1, the delivery end of anextruder is illustrated fragmentarily. Said extruder plasticates andhomogenizes synthetic resin of desired composition and discharges thesame at a substantially uniform rate through inlet opening 12 in theparison head 14. The parison head is provided with an internal cavity 16within which a mandrel 18 is mounted to control the flow rate of resindelivered to the discharge end 20 of the parison head 14. In accordancewith customary construction, the mandrel 18 is adjustable longitudinallya limited amount within the internal cavity 16 when the mold system isbeing set up for a given run, by a diagrammatically illustratedadjusting nut 22. Longitudinally movable within the mandrel 18 is a diepin 24 which moves cyclically in opposite directions by a control means,not shown, connected to the projecting end 26 of the die pin 24. Suchcyclical movement of the end of the die pin adjacent the discharge end20 of the parison head is programmed to control the contour of theparison 28 which is progressively discharged from the parison head 14for disposition between successive pairs of molding dies 30 and 32.

In the exemplary illustration of the molding mechanism shown in FIG. 1,it will be seen that the parison 28 is discharged substantiallyvertically upward due to the fact that the molding dies 30 and 32 alsomove upward after the same have been moved transversely into abutmentwith each other so as to enclose a section of the parison therebetween.The molding dies 30 and 32 are movable toward and away from each otherby mechanism, not shown, which is connected to the supporting bars 34and 36 which represent the supporting and actuating means for themolding dies in exemplary manner.

A plurality of pairs of such molding dies 30 and 32 are shown mounted onan examplary Ferris wheel 34, the arrangement of which with respect tothe extruder l0 and parison head 14 being shown in small scale inexemplary manner in FIG. 2. The direction of rotation thereof also isillustrated by directional arrows shown in said figure whereby it willbe seen that the delivery of the parison from the head 14 will beengaged by the pair of mold-ing dies 30 and 32 immediately above thesame while moving substantially in a vertical direction. While they areso moving, they respectively are moved toward each other to enclose asection of the parison 28 therebetween for subsequent molding of ahollow article therefrom by the following means and method.

In FIG. 1, the molding dies 30 and 32 are shown to have supplementarycavities 36 and 38 therein which, as illustrated, are substantiallymirror images of each other, whereby they supplement each other to forma single mold cavity 40. The upper and lower ends of the die cavities 36and 38 respectively are provided with cooperating rim means 42 and 44which function to pinch a section 46 of predetermined length of theparison 28 and thereby seal the opposite ends of said section, as wellas provide a breaking point for separation of waste sections of theparison such as section 48 from the completely molded object.

Immediately upon the closing of the molding dies 30 and 32 upon thesection 46 of the parison, a blow needle 50 pierces thesegregatedsection 46 and instantly inflates it while the parison is in asubstantially vertical position. Due to the fact that the parison isapproximately at its melting point, if not a few degrees above it atthis stage, it is sufficiently plasticated that it will evenly expandtransversely into conformity with all surfaces of the die cavities 36and 38, whereupon the hollow article thus formed has walls ofsubstantially uniform thickness and commences to be chilled by thecontrolled temperature of the molding dies 30 and 32.

While the foregoing description includes certain features of noveltywhich are described and claimed in said aforementioned relatedapplications, the details thus far described pertain to the presentinvention only in a general way. The principal features andcharacteristics of the invention are set forth as follows.

Referring to FIG. 5, there is shown an exemplary fragmentary sectionalelevation of the lower portions of a pair of conventional dies employedin existing blow molding machines. In said figure, the molding dies 52and 54 have cavities 56 and 58 which also are of conventional nature.The lower portions of the molding cavities S6 and 58 terminate intapered rim means 60 and 62 which pinch the parison 64 incident toclosing one end of a segregated section of the parison, similar tosection 28 illustrated in FIG. 1, immediately prior to the segregatedsection of the parison being inflated into molded engagement with themolding cavities 56 and 58.

It is known that when a parison is pinched by conventional rim means 60and 62 of the type generally illustrated in FIG. 5, there is a tendencyfor part of the resin to be drawn away from the inner surface of themolded wall 66 of the hollow article 68 and thereby form a lineardepression 70 which extends diametrically across said wall 66 betweenopposite side walls of the hollow article 68, in the form of a groove.When the waste portion of the parison 64 is separated from the moldedwall 66 at the completion of molding of the hollow article 68, it willbe seen that the diametrical portion of the molded wall along the grooveor linear depression 70 comprises a weakness therein. In view of theinherent formation of such a groove, it is customary to supplement thestrength of the molded wall 66 by increasing the thickness thereof tosuch extent that the portion of said wall in the vicinity of thedepression 70 will be sufficiently strong to withstand any stresses towhich the molded article is intended to be subjected. This results inusing excess raw material and also frequently produced bubble-likeformations at the end of the groove or seam.

The present invention obviates the aforementioned difficulty which isinherent in products produced by molding dies in the type shown in FIG.5 by providing what is referred to as a mold dam arrangement, details ofwhich are best shown in FIGS. 3 and 4 due to the larger size of thescale therein as compared with that of FIG. I. Said dam means comprisesa pair of ribs 72 which respectively are provided on the adjacent facesof molding dies 30 and 32. Said ribs are parallel to and spaced a shortdistance below the rim means 44 on said end of said molding dies. Itwill be seen that the operative faces'of the ribs 72 also areappreciably wider than the rim means 44.

When the molding dies 30 and 32 are brought together to encircle thesection 46 of the parison 28, the ribs 72 will engage and compress apredetermined length of the parison 28 to segregate a short section 74of the parison resin within transversely extending cavities in the diesbetween the ribs 72 and the rim means 44 which is substantially solidresin devoid of any entrapped air, as can seen from FIG. 4. In doing so,a portion of the segregated short section 74 will be forced through thespace between the rim means 44, before they close to their full extent,whereby a small amount of additional resin is available to be forcedinto the transverse wall 76 of a molded hollow object 78 in such mannerthat said transverse wall 76 will be of substantially uniform thicknessover the entire area thereof, including the area which is immediatelyabove the rim means 44, assuming that said wall is designed to haveoverall uniform thickness.

From the foregoing, it will be seen that by forcing a slight amount ofadditional plasticated resin upwardly from the ribs 72 during theclosing of the molding dies upon each other, it is possible to conservethe additional amount of resin which heretofore has been required toproduce a transverse wall in a molded hollow article of adequatestrength in accordance with the procedure described above with respectto FIG. 5, whereby in accordance with the present invention, thetransverse wall 76 shown in FIG. 4 need have no greater thickness thanthat of the sidewalls of the molded hollow object 78, for example,unless greater thickness is so desired. Thus, a small but noticablesaving in raw material is possible by utilizing the present invention inthe formation of hollow molded resin articles having transverse walls inat least one end thereof, or similar structure, in regard to the makingof which the present invention may be employed.

While the invention has been described and illustrated in its severalpreferred embodiments, it should be understood that the invention is notto be limited to the precise details herein illustrated and describedsince the same may be carried out in other ways falling within the scopeof the invention as illustrated and described.

I claim:

1. Dies for forming hollow articles from synthetic resin by positioninga plasticated resin parison between a pair of mold dies and blowing saidparison internally into conformity with the cavities in said dies, saiddies having cavities therein supplementary to each other to form ahollow article of desired configuration, one end portion of each cavitybeing adapted to form a substantially transverse wall at one end of saidarticle, and rim means on said dies adjacent the opposite ends of saidcavities therein operable to pinch a parison at spaced locations to forma sealed section thereof to be blown into conformity with said moldcavity, one of said pinched portions of said parison forming a seamacross said transverse wall of articles blown in said cavities of saiddies when in operative abutment, in combination with transverselyextending rib means on said dies spaced from said rim means of said oneend portion of each mold cavity and substantially within the plane ofsaid rim means to define correspondingly extending narrow cavitiesshaped and operable when said dies are moved into abutment to force aportion of said parison into entrapment within said narrow cavities andcompress it into a mass substantially devoid of cavities and force someof said mass past said rim means while the dies are closing and intosaid one end portion of each mold cavity to provide an adequatesupplemental amount of resin at the seam in said one end of a blownmolded article to produce a seam section at least as thick as theadjacent portions of said end of said articles.

2. The dies according to claim 1 in which said rib means extendtransversely to the axis of said die cavity and are at least as long asthe width of said parison when compressed therebetween.

3. The dies according to claim 1 in which said ribs have a width in anaxial direction relative to said mold cavities greater than the width ofthe rim means on the mold cavity adjacent said ribs, whereby the widthof said ribs is effective to compress the portion of parison engagedthereby in opposite longitudinal directions, one of which directionsextends toward said adjacent rim means to provide said aforementionedadequate amount of resin.

I! t t

1. Dies for forming hollow articles from synthetic resin by positioninga plasticated resin parison between a pair of mold dies and blowing saidparison internally into conformity with the cavities in said dies, saiddies having cavities therein supplementary to each other to form ahollow article of desired configuration, one end portion of each cavitybeing adapted to form a substantially transverse wall at one end of saidarticle, and rim means on said dies adjacent the opposite ends of saidcavities therein operable to pinch a parison at spaced locations to forma sealed section thereof to be blown into conformity with said moldcavity, one of said pinched portions of said parison forming a seamacross said transverse wall of articles blown in said cavities of saiddies when in operative abutment, in combination with transverselyextending rib means on said dies spaced from said rim means of said oneend portion of each mold cavity and substantially within the plane ofsaid rim means to define correspondingly extending narrow cavitiesshaped and operable when said dies are moved into abutment to force aportion of said parison into entrapment within said narrow cavities andcompress it into a mass substantially devoid of cavities and force someof said mass past said rim means while the dies are closing and intosaid one end portion of each mold cavity to provide an adequatesupplemental amount of resin at the seam in said one end of a blownmolded article to produce a seam section at least as thick as theadjacent portions of said end of said articles.
 2. The dies according toclaim 1 in which said rib means extend transversely to the axis of saiddie cavity and are at least as long as the width of said parison whencompressed therebetween.
 3. The dies according to claim 1 in which saidribs have a width in an axial direction relative to said mold cavitiesgreater than the width of the rim means on the mold cavity adjacent saidribs, whereby the width of said ribs is effective to compress theportion of parison engaged thereby in opposite longitudinal directions,one of which directions extends toward said adjacent rim means toprovide said aforementioned adequate amount of resin.